"It's really hard to say if people drink quality bottled water," said Gu Zhenhua, deputy director of the Shanghai Health Supervision Office.

Bottled water began to enter people's lives in the mid 1990s, and it almost brought a revolution. Known as a cleaner alternative, bottled water soon outshone smelly tap water.

But people who turn to bottled water may not like to know that clean water from bottles without harmful bacteria contains no health-giving trace elements.

"Filtration gets rid of almost everything in the water, bad or good," Gu said. Some experts warn people not to drink bottled water.

In Gu's eyes, as long as one has a balanced diet and is not choosy about food, his nutritional structure cannot be easily changed by drinking bottled water.

"The channel for having such trace elements is by no means only through drinking bottled water," he said. "Different kinds of foods can also supply such nutrition. And the water going into one's body is not only pure water; most households still use tap water for cooking."

With the discussion still going on, local government is trying to achieve another goal: making it possible to drink water directly from the tap.

"If the water just keeps flowing in the pipe, that's OK," said Chen Ping, director of the quality control department at Shanghai Aquarius Drinking Water Co. "But what if the tap is not touched for hours, or even for days?"

The water remaining in the pipes becomes one of the biggest concerns.

"Not turning the tap for quite some time is possible, and it may frequently happen in many families," Chen said. "Water may deteriorate in the pipes."

In some residential quarters, which have been picked as pilot communities for high quality water, although circulation technology has been applied to keep the water fresh in the pipe, some still worry whether all the water in the pipe can be renewed.

"That is a question. Can the circulating water pass through every valve and reach the tap?" she said. "Bacteria may find a living enironment in places where circulating water cannot reach."

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